Avantes USB spectrometers are supplied with a Windows binary which generates one ROH and one RCM file when the user clicks "Save experiment". In the version of 6.0, the ROH file contains a header of 22 four-byte floats, then the spectrum as a float array and a footer of 3 floats. The first and last pixel numbers are specified in the header and determine the (length+1) of the spectral data. In the tested files, the length is (2032-211-1)=1820 pixels, but Kaitai determines this automatically anyway.
The wavelength calibration is stored as a polynomial with coefficients of 'wlintercept', 'wlx1', ... 'wlx4', the argument of which is the (pixel number + 1), as found out by comparing with the original Avantes converted data files. There is no intensity calibration saved, but it is recommended to do it in your program - the CCD in the spectrometer is so uneven that one should prepare exact pixel-to-pixel calibration curves to get reasonable spectral results.
The rest of the header floats is not known to the author. Note that the newer version of Avantes software has a different format, see also https://www.mathworks.com/matlabcentral/fileexchange/37103-avantes-to-matlab
The RCM file contains the user-specified comment, so it may be useful for automatic conversion of data. You may wish to divide the spectra by the integration time before comparing them.
Written and tested by Filip Dominec, 2017-2018
This page hosts a formal specification of Avantes USB spectrometer ROH file 6.0 using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
digraph {
rankdir=LR;
node [shape=plaintext];
subgraph cluster__avantes_roh60 {
label="AvantesRoh60";
graph[style=dotted];
avantes_roh60__seq [label=<<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0">
<TR><TD BGCOLOR="#E0FFE0">pos</TD><TD BGCOLOR="#E0FFE0">size</TD><TD BGCOLOR="#E0FFE0">type</TD><TD BGCOLOR="#E0FFE0">id</TD></TR>
<TR><TD PORT="unknown1_pos">0</TD><TD PORT="unknown1_size">4</TD><TD>f4le</TD><TD PORT="unknown1_type">unknown1</TD></TR>
<TR><TD PORT="wlintercept_pos">4</TD><TD PORT="wlintercept_size">4</TD><TD>f4le</TD><TD PORT="wlintercept_type">wlintercept</TD></TR>
<TR><TD PORT="wlx1_pos">8</TD><TD PORT="wlx1_size">4</TD><TD>f4le</TD><TD PORT="wlx1_type">wlx1</TD></TR>
<TR><TD PORT="wlx2_pos">12</TD><TD PORT="wlx2_size">4</TD><TD>f4le</TD><TD PORT="wlx2_type">wlx2</TD></TR>
<TR><TD PORT="wlx3_pos">16</TD><TD PORT="wlx3_size">4</TD><TD>f4le</TD><TD PORT="wlx3_type">wlx3</TD></TR>
<TR><TD PORT="wlx4_pos">20</TD><TD PORT="wlx4_size">4</TD><TD>f4le</TD><TD PORT="wlx4_type">wlx4</TD></TR>
<TR><TD PORT="unknown2_pos">24</TD><TD PORT="unknown2_size">4</TD><TD>f4le</TD><TD PORT="unknown2_type">unknown2</TD></TR>
<TR><TD COLSPAN="4" PORT="unknown2__repeat">repeat 9 times</TD></TR>
<TR><TD PORT="ipixfirst_pos">60</TD><TD PORT="ipixfirst_size">4</TD><TD>f4le</TD><TD PORT="ipixfirst_type">ipixfirst</TD></TR>
<TR><TD PORT="ipixlast_pos">64</TD><TD PORT="ipixlast_size">4</TD><TD>f4le</TD><TD PORT="ipixlast_type">ipixlast</TD></TR>
<TR><TD PORT="unknown3_pos">68</TD><TD PORT="unknown3_size">4</TD><TD>f4le</TD><TD PORT="unknown3_type">unknown3</TD></TR>
<TR><TD COLSPAN="4" PORT="unknown3__repeat">repeat 4 times</TD></TR>
<TR><TD PORT="spectrum_pos">84</TD><TD PORT="spectrum_size">4</TD><TD>f4le</TD><TD PORT="spectrum_type">spectrum</TD></TR>
<TR><TD COLSPAN="4" PORT="spectrum__repeat">repeat (((ipixlast).to_i - (ipixfirst).to_i) - 1) times</TD></TR>
<TR><TD PORT="integration_ms_pos">...</TD><TD PORT="integration_ms_size">4</TD><TD>f4le</TD><TD PORT="integration_ms_type">integration_ms</TD></TR>
<TR><TD PORT="averaging_pos">...</TD><TD PORT="averaging_size">4</TD><TD>f4le</TD><TD PORT="averaging_type">averaging</TD></TR>
<TR><TD PORT="pixel_smoothing_pos">...</TD><TD PORT="pixel_smoothing_size">4</TD><TD>f4le</TD><TD PORT="pixel_smoothing_type">pixel_smoothing</TD></TR>
</TABLE>>];
}
avantes_roh60__seq:ipixlast_type -> avantes_roh60__seq:spectrum__repeat [color="#404040"];
avantes_roh60__seq:ipixfirst_type -> avantes_roh60__seq:spectrum__repeat [color="#404040"];
}